Tetrafluoroterephthalic acid difluoride is useful as a synthetic intermediate of agrichemicals (e.g. EP 140482 A). As a method for producing tetrafluoroterephthalic acid difluoride, a method comprising reacting tetrachloroterephthalic acid dichloride with potassium fluoride in the absence of a solvent (e.g. Probl. Organ. Sinteza, Akad. Nauk SSSR, Otd. Obshch. i Tekhn. Khim. (1965), p. 105-108), a method comprising reacting tetrachloroterephthalic acid dichloride with potassium fluoride in the presence of sulfolane, digylme, diphenyl sulfone, nitrobenzene, N,N-dimethylacetamide, N-methyl-2-pyrrolidone or benzonitrile (e.g. EP 140482 A), a method comprising reacting tetrachloroterephthalic acid dichloride with potassium fluoride in sulfolane using calixarenes as a catalyst (e.g. CN 1458137 A), and the like have been known.